MicroLogix 1000 fault light blinking

[lesmar96]

Hey Folks,
I have a customer with an older machine that is controlled with a MicroLogix 1000. The machine just quit working.

The power light is on solid, the run light is off, the fault light is blinking, and the force light is off. Obviously something is not right if the fault lights is blinking and the run light is off, but what?

I'd appreciate help from all you AB fellows! Thanks!

 

[OkiePC]

It is probably a recoverable fault. If power cycling does not clear it, then you may need to go online using RSLogix 500 (or RSLogix Micro) to find more details. I have not worked with the ML1000 much in the last 10 years or so, but it has been my experience that they are really rugged but can lose their program if there are significant power quality issues. A flashing fault LED is much better news than a solid red fault.

 

[shawn_75]

It's likely the retentive data lost error. It happens a lot on the ML1000. You have to go online and clear the fault. In addition to clearing the fault, you need to manually reset one of the error bits for this particular error.

 

[lesmar96]

Thank you for your help and sorry for my delayed response. We were able to log in to it. it still had the program but was faulted because a timer preset was written to 0.

The odd thing was there is no HMI or any other way for the operator to change timer presets. We figured it is failing, it is definitely old.

 

[kolyur]

A timer preset of zero will not cause a fault. In fact, this is a quick way to disable a timer during testing or troubleshooting. I think the source of your fault must be something else.

 

[I_Automation]

I agree with kolyur, maybe it actually said "timer preset LESS than zero'

A negative preset will fault a PLC.

Either that or it is beginning a hardware/firmware fault and this is a good time to get a spare and program it.

 

[geniusintraining]

I would also put an unconditional OTU S:5/0 as the last rung of file 2, just to be on the safe side

 

[lee1968nh]

I timer preset of <0 will cause a fault, however. IMO, it shouldn't but it does.

 

[lesmar96]

I agree with kolyur, maybe it actually said "timer preset LESS than zero'

A negative preset will fault a PLC.

Either that or it is beginning a hardware/firmware fault and this is a good time to get a spare and program it.

I was not the one actually logged in so I may not have relayed this information correctly. It could have been <0.

But this is the approach we took. The customer agreed hardware is likely failing. We have programmed a 1400 and swapped it out.

Thanks for help. Been so busy hardly have time to reply.

 

[harryting]

I had dealing with one or two Micro 1000 in my life. All I remember is that is that they have a tendency to fault.

 

[lee1968nh]

Wasn't your fault.

 

[roxusa]

I always suggest when going online to a faulted processor not to "clear error"
but to "go to error" and check what the error is before clearing it. I've seen the
retentive data loss error as Shawn 75 pointed out a lot with the ML-1000. I was told poor power supply or not good suppression on AC outputs.

 

[alive15]

I would also put an unconditional OTU S:5/0 as the last rung of file 2, just to be on the safe side

Could you expound on the reasoning behind this? I have seen this trick given on other threads, but never found some explanation for it. Why specifically at the end of Lad 2? And what is the output that it unlatches?

 

[roxusa]

I put the "OTU S:5/0" at the end of my last ladder, it resets the math overflow and prevents a minor error from faulting the processor in the event you have some condition
that is causing an overflow such as counting to high ect. It doesn't correct the problem just stops you from faulting on that cause, you should still correct the math.

 

[James Mcquade]

OTU s:5/0 is the overflow / underflow status bit.
any time this bit is set, it will cause a minor fault in the plc and halt the program.
you put this rung as the last rung of a program in the main ladder to prevent this fault from faulting the plc program.
I always use this method.
when you multiply 2 numbers you use s13 and s14. if the result is greater than 32767, you create a fault. this is especially true in older slc plc's that do not have the scp instruction. counters that count off a prox can also cause this.
the result is a minor fault, but the plc program continues to run.
james